<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>CSS-ID选择器</title>
    <style>

        /*Ctrl + D 复制当前行到下一行*/
        /*Ctrl + Y 删除当前行*/
        #td1{
            background-color: red;
        }
        #td2{
            background-color: yellow;
        }
        #td3{
            background-color: gray;
        }
        td{
            background-color: deeppink;
        }s
    </style>
</head>
<body>

<!--table 给高度是没效果的.具体的高度要靠内容撑起来-->
<table width="50px" height="50px">
    <tr>
        <td id="td1"></td>
    </tr>
    <tr>
        <td id="td2"></td>
    </tr>
    <tr>
        <td id="td3"></td>
    </tr>
</table>
</body>
</html>